Viruses were isolated from each of five different HIV-1 clinical patients on one or as many as three occassions at least six months apart. A total of nine clinical isolates were recovered and each was grown in H9 cells to make a virus pool. Six to ten serum samples from these same five patients were also collected at six month intervals over a period of 2.5-5 years. Sera were tested against their autologous virus isolates to determine if there is a change is neutralizing antibody (NA) titers before and after the virus isolation. No change was evident, however virus isolates from the same patient varied greatly with respect to NA titers. One of the patients that had virus isolated on two occassions one year apart, initially had titers of 1:128-1:256 but the titers against the second isolate were 1:8192-1:16384 which showed that this new virus was easily neutralized. In another patient where three isolates were recovered at six month intervals, the first isolate was highly resistant to neutralization by autologous sera with titers of <1:16, however, the second and third isolate had titers ranging from <1:16-1:64. This data shows that virus isolated from the same patient at different times has distinct patterns of NA activity. These isolates will be further studied by PCR to see if the change in amino acid sequence of the virus envelope glycoprotein can be determined and whether these differences occur within or outside of the V3 loop region of the gp120 which is the region known as the principal neutralizing determinant.